Process for treating by-product oils produced in the production of olefins

ABSTRACT

THERMALLY STABILIZED OIL FRACTIONS AND PITCH FRACTIONS ARE OBTAINED FROM BY-PRODUCT OILS IN THE PRODUCTION OF OLEFINS WHICH COMPRISES HEATING THE BY-PRODUCT OILS AT 400-600*C. FOR 10-1200 SECONDS UNDER A PRESSURE OF 20-2000 KG./CM2 TO FORM THERMALLY STABILIZED OIL FRACTIONS AND RESIDUE FRACTIONS AND THEN TREATING THE RESIDUE FRACTIONS AT 300-480*C., UNDER A PRESSURE OF FROM NORMAL PRESSURE TO 50 KG./CM.2 FOR 1-10 HOURS TO PROVIDE USEFUL PITCH FRACTIONS.

Feb. 26, 1974 SATORU ENOMOTO ETAL 3,794,579

PROCESS FOR TREATING BY'PRODUCT OILS PRODUCED IN THE PRODUCTION OF OLEFINS Filed Dec. 29, 1972 FIG. I

FIG. I

United States Patent Int. 01. Cine 3/00 US. Cl. 208-40 Claims ABSTRACT OF THE DISCLOSURE Thermally stabilized oil fractions and pitch fractions are obtained from by-product oils in the production of olefins which comprises heating the by-product oils at 400-600 C. for 10-1200 seconds under a pressure of 20-2000 kg./cm. to form thermally stabilized oil fractions and residue fractions and then treating the residue fractions at 300480 C., under a pressure of from normal pressure to 50 kg./cm. for 1-10 hours to provide useful pitch fractions.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to a process of treating by-product oils having boiling points of higher than 150 C. obtained during the production of olefins, and more particularly, the invention relates to a process of recovering useful thermally stabilized oil fractions and pitch fractions from the by-product oils obtained during the production of olefins.

Description of the prior art With the recent rapid developments in petroleum chemistry, installations for producing olefins, in particular ethylene, have increased, and the amount of byproduct residual oils from the production of olefins by thermal cracking has also increased rapidly. These byproduct oils have only partially been used as a raw material for the production of carbon black and have mostly been used as fuels. Therefore, more effective uses of such by-product oils have been desired by the art.

SUMMARY OF THE INVENTION One object of this invention is to provide a process for effectively utilizing by-product oils obtained in the production of olefins as described above, i.e., the primary object of this invention is to provide a process of treating such by-product oils to provide thermally stabilized oil fractions mainly composed of low boiling fractions such as naphthalene and methyl naphthalene and pitch fractions mainly composed of polycyclic aromatics.

The above object of this inventionhas been attained according to the process of this invention wherein the by-product oils having boiling points of higher than 150 C. obtained in the production of olefins are initially treated at temperatures of from 400-600 C. for"10 1200 seconds under a pressure of 20-200 kg./cm. the by-product oils thus treated are then separated into thermally stabilized oil fractions and residue fractions by means of flashing or distillation, and then the residue fractions are treated at temperatures of 300-480 C. for 1-10 hours under a pressure of from normal pressure to 50 kg./cm. to provide pitch fractions or components.

by-product oils obtained in the production of olefins, the' 3,794,579 Patented Feb. 26, 1974 "ice by-product oils having a boiling point range of 180- FIG. 2 shows a gas chromatographic analysis of the oil fractions obtained by the process of this invention 1n the same boiling point range.

DETAILED DESCRIPTION OF THE INVENTION The oils used as a starting material in this invention are by-product oils in the production of olefins which means so-called ethylene bottom oils obtained in the case of producing olefins such as ethylene, propylene, etc.,

by thermally cracking light fractions of petroleum oil such as naphtha, kerosene, light oil, etc., at 700-950" C. by means of an outer-heating type tubular reactor, and also oils having a high content of aromatic compounds and mainly containing fractions having a boiling point higher than 150 C. obtained by various thermal crackings or-catalytic crackings of petroleums. Those by-product oils have different properties depending on the conditions of cracking and the conditions of any distillations after cracking, but such changes of properties give no problems to the practice of the process of this invention. However, particularly preferred by-product oils are those having a high content of aromatic compounds and which contain more than 80% of fractions having boiling points higher than 200 C.

The heat treatment which is the first step of this invention has been developed as a means of improving the faults of conventional treatments for =by-product oils generated in the production of olefins, e.g., when the by-product oils are subjected to a distillation or a heat treatment at normal pressure only pitch having a low aromaticity is obtained by the polymerization of unsaturated bond portions and, since such by-product oils largely contain unsaturated bonds and alkyl side chains, the oil fraction obtained with conventional processes contains various alkyl groups and cannot be considered thermally stabilized.

More specifically, according to the heat treatment of the first step of this invention the lay-product oils are heated at temperatures of 400-600 C. for 10-1200 secs. under a pressure of 20-200 kg./cm. whereby the unsaturated bond portions of the by-product oils are thermally decomposed and stabilized, and at the same time the various alkyl chains are removed to provide oil fraction highly enriched with aromatics. The above heat treatment is more preferably conducted at temperatures of 440-580 C. for 30-500 seconds and under a pressure of 50-150 kg./cm.

By the heat treatment, the content of the unsaturated bond portions, the unstable portions in the by-product oils, is greatly reduced and, at the same time, the long alkyl side chains are decomposed to provide high aromaticity. The heat treatment requires no specific equipment and can be conducted using a conventional reactor such as a flow-type reactor. If desired, the above heat treatment may be conducted in two to four stages.

The second step operation in this invention comprises removing gaseous materials formed in the previous heat treatment and, at the same time, separating the thermally stabilized oil fractions or components from the residue fractions or components by any acceptable separation 3 whereby pitch fractions having a polycyclic aromatic structure are obtained.

The above steps in the process of this invention are necessary for attaining the objects of this invention, i.e., to obtain thermally stabilized oil fractions and pitch fractions enriched with polycyclic aromatics from by-product oils obtained in the production of olefins, and thus all of the steps of this invention must be practiced to obtain the results of the present invention. For example, if the first step and the second step indicated above are omitted in the three-step process of this invention, the oil fractions obtained are poor in thermal stability and further the pitch fractions obtained contain a low content of aromatics. Furthermore, in such a case the content of quinoline insoluble portions becomes larger due to the occurrence of locally heterogeneous polycondensations, and thus an excellent pitch cannot be obtained. Also, if the first heat-treatment step is conducted under other conditions than those of this invention, the thermal stability of the oil fractions formed is insufficient, and thus only the heretofore described undesirable results are obtained. Further, in certain cases, a carbonization or coking occurs during the reaction which makes it impossible to further continue the reaction.

When light fractions having boiling points lower than 400 C. are removed from the pitch fractions obtained by the process of this invention by a distillation, a pitch showing the excellent properties given in Table 1 is obtained. This pitch differs greatly from conventional coal pitches and petroleum pitches in various physical properties and in its polycyclic aromatic structure. Further, the pitch thus obtained has a high softening point, it contains a large proportion of benzene insoluble material but a very low proportion of quinoline insoluble material. Fnally, the carbonization yield is high.

TABLE 1PITCH PROPERTIES Hydrogen/carbon ratio (H/C) by elementary analysis 0.8-0.5. Boiling point 400 C. Softening point (ring and ball test) 140-230 C. Benzene insoluble materials 15-60%. Quinoline insoluble materials Less than 20%. carbonization yield 4070%.

alkyl side chains have been decomposed, they can be used as intermediate raw materials for insulating oils, various solvents, etc. In particular, the oil fractions con tain mainly naphthalene and methyl naphthalene as the low boiling components thereof, and these components can be easily separated as compared with the original by-product oils.

As mentioned above, by treating the by-product oils obtained in the production of olefins, which by-product oils contain many components, according to the process of this invention, the oil fraction obtained can be used as intermediate materials and excellent pitch fractions are obtained. The process of this invention thus has great industrial significance.

The invention will now be illustrated in greater detail by several examples.

EXAMPLE 1 The by-product oil (so-called ethylene bottom oil) having the properties shown in Table 2 which was obtained in the production of olefins was subjected to a series of the first step reactions at the conditions shown in Table 3 in a flow-type tubular reactor having a diameter of 3.35 mm. and a length of 8 meters.

In addition to clearly showing the effect of the reaction in the first step, the reaction product in the first step reaction was partially recovered and the bromine value and the H/C ratio of the residue fractions having boiling points higher than 400 C. were measured as factors representative of the content of unstable portions and the side chain content, respectively. The results of such measurements are also shown in Table 3. Further, a series of comparison experiments were conducted under conditions other than those of this invention, the results being shown in Table 3 as the S-Series.

Reaction conditions at- Properties of product obtained Pres- Fractions, percent at sure, Amount Brokg. Temp Time of gas mide -250 250-350 360-400" 400 Residue cm. C (sec.) 1 ll. feed value 0. C. C. 0. BIG

Invention- 50 510 35 5. 0 13. 8 41. 0 16. 0 7. 0 36. 0 0. 70 150 510 35 3. 1 11. 0 46. 0 8. 0 11. 0 35. 0 0. 68 150 480 35 3. 7 13. 6 44. 0 10. 0 11. 0 35. 0 0. 70 150 550 35 20. 1 9. 0 52. 0 7. 0 14. 0 27. 0 0. 150 600 35 32. 0 7. 3 52. 0 5. 0 13. 0 30. 0 0. 63 160 510 1 35x2 6. 4 7. 9 50. 0 7. 0 11. O 32. 0 0. 65 150 510 3 X3 40. 0 6. 8 53. 0 5. 0 9. 0 33. 0 0. 62 150 510 600 190. 0 6. 5 53. 0 5.5 5. 5 36. 0 0.59 150 560 35 31. 0 7. 0 51. 0 6. 0 11. O 32. 0 0. 64 150 560 72 63. 0 6. 6 53.0 5. 0 6. 0 36. 0 0. 60

TABLE 3Continued Reaction conditions at-r pert s. pr u t ob ned Pres- Fractions, percent atsure, 1 Amount Bro-.

kg./ Ten, Time of gas, mlde -250 250-350 350-400 400 Residue cm. 2 (see.) 1./1. feed value 0. C. C. C H/O Comparison- Run N o: I

S-l 510 35 Cokmgand clogging occurred S-2 10 510 35 -3- 380 35 0. 2 62. 1 39. 0 14. 5 6.5 40. 0 1. 02 S-4 380 35 0. 3 61. 8 38. 5 16. 3 7. 2 38. 0 1. 03 S5- 30 510 5 0. 4 53. 2 39. 0 16. 0 7. 0 38. 0 1. 01 8-6.- 150 380 35 0. 3 62. 8 37. 0 15. 0 8. 0 40. 0 1. 03 S- 150 380 700 0. 9 48. 5 40. 0 l6. 0 9. 0 35. 0 0. 96 8-8 150 600 5 1. 7 37. 1 42. 0 14. 0 7. 5 36. 5 0. 87 2:? g 1 30(5) Coking and clogging occurred Control Non-treated 65. 4 38. 0 15. 0 6. O 41. 0 1. 08

1 Run F was a two-stage operation in which the first heat treatment was conducted for 35 seconds and then the same procedure was conducted thereafter.

1 Run G same procedure was repeated twice thereafter.

8 Normal pressure.

As is clear from Table 3, in the reaction products formed by treating under the conditions of the invention, the bromine values were greatly reduced as compared with those of the untreated by-product oils, and thus it will be easily understood from this fact that the proportion of unsaturated portions was reduced as a result of decomposition. Further, the H/C ratio of the residues was less than 0.75 in any case Where treatment was under the conditions of this invention, which shows that the side chains had been decomposed and at the same time converted into polycyclic structures by a polycondensation reaction.

0n the other hand, in the comparison runs shown in the above table as the S-series, coking occurred during Runs S-1 and S2 wherein the temperature and the time were within the invention but the pressure was lower than required in this invention, and it became impossible to continue the reaction in both runs. In Runs S-3 and 8-4 where the temperature was lower than required in this invention, the bromine value and the H/C ratio were almost the same as those of the raw materials and thus the effect of the heat treatment was not observed in either case. In Runs S-5 and 8-8 where the pressure and the temperature were in accordance with this invention but the reaction time was shorter than the time range of this invention, neither the bromine value nor the H/C ratio was improved. In Runs S-6 and 8-7 where the pressure and the reaction time were within the scope of this invention but the reaction temperature was lower than required in this invention, almost no effect of the treatment was observed. Moreover, in Run S-10 where the pressure and the reaction temperature were within the scope of this invention but the reaction time was longer than that of the invention, and in Run S-9 where the pressure was Within the scope of this invention but the reaction was conducted at a temperature outside the scope of this invention for a shorter time than required in this invention, coking occurred to clog the pipe of the reactor, and it was difiicult to further continue the run in each case.

Then, each product obtained from the first step of the process of the present invention was subjected to the second or the separation step of the present invention at the conditions described in Table 4 in order to remove low boiling materials and recover the oil fractions. T hereafter the residue fractions were subjected to the heat treatment of the third step of the present invention at the conditions shown in Table 4.

The oil fractions recovered in the second or separation step had, although the properties were slightly influenced by the conditions for the separation, a boiling range of 70-350 C., a specific gravity range of 0.9-4.0, and a refractive index range of lower than 1.68. Various physical measurements confirmed that they were aromatic oils having no long side chains. Among the oil fractions, the fractions having a boiling point range of 210-250" C. were almost totally composed of naphthalene and methyl naphthalene, and the two components could be easily separated from each other. This feature will further be was a three-stage operation in which the first heat treatment was conducted for 70 seconds and the explained by referring to the accompanying drawings. FIG. 1 is a gas chromatographic chart of the raw materials or the by-product oils in the same boiling point range and FIG. 2 is a gas chromatographic chart of the oil fractions obtained by the process of this invention in the same boiling point range. The gas chromatographic measurements were carried out with a K-53 Type Gas Chromatographic Analyzer made by Hitachi Ltd. under the following conditions: the length of the capillary column was 45 meters, the filler was Q-45 (silicone oil), the measurement temperature was C., the carrier gas was nitrogen and a flame ion detector (FID) was used.

As is clear from the drawings, the many peaks of various compounds observed in FIG. 1 were not observed in FIG. 2, which clearly shows the effect of the heat treatment of the first step. In addition, in the gas chromatographic analysis it is clear that many components having a boiling point in the range of 250-320 C. in the raw material converted into dimethyl naphthalene, biphenyl, etc.

The yield of oil fractions in this invention depends upon the properties of the raw materials, the conditions for the first process step, the separation conditions etc., but in general the yield is 30-50% by weight based on the amount of the raw materials. The yield of naphthalene and mcthylnapthalene fractions was 20-40% by weight based on the amount of raw materials and the content of the two components in the oil fractions was in the range of 40-90% by weight of the weight of the oil fractions.

To clearly show the effect of this invention, the pitch fractions obtained in the heat treatment of the third step were treated to remove low boiling materials having boiling points of lower than 400 C., and the properties of the pitches thus obtained were measured, the results of which are shown in Table 4.

As is clear from Table 4, the pitch obtained by the process of this invention had excellent properties, for example, the-carbonization yield was high, the content of benzene insoluble components was high, the content of quinoline insoluble components was low, and the softening point was high. On the other hand, as is clear from the comparison tests shown in Table 4 as the T-Series Runs, which were conducted under conditions outside the scope of this invention, good results could not be obtained,

In Runs T-2 and T-3 in which the conditions for the first step and the second step were within the scope of this invention but the conditions for the third step were I outside the scope of this invention. an increase of quino line insoluble material caused by the prolongation of the reaction period was observed in the former, and no increase of benzene insoluble material was observed in the latter where the reaction time was too low. Furthermore,v

when the conditions for the first treatment step were outside the scope of this invention, the increase of quino- TABLE 4. CONDITIONS FOR 2ND AND 3RD STEPS AND PROPERTIES OF PITCH PRODUCED Conditions for 3rd step Properties of pitch Conditions Pres- Benzene Quinoline Soft- Carbonfor 2nd step condition sure, insoluble insoluble ening ization 1st for separating step, kg./ Temp Time, matter, matter, point, yield, step temp., C. cm. hrs. H/C percent percent percent Invention-Run N 0.:

1 50 350 0. 65 28.4 t 172 56. 3 450 1 0. 62 35. 2 0. 8 184 58. 9 400 5 0. 58 38. 5 t 200 65. 1 380 3 0.56 49. 8 t 201 66. 8 380 3 0. 57 51. 0 t 198 66. 1 400 5 0. 54 43. 2 t 208 62. 5 400 5 0. 55 44. 4 t 215 64. 2 380 2 0. 55 48. 6 t 208 64. 1 380 3 0. 65 30. 0 t 175 58. 5 420 4 0. 58 53. 4 1. 5 213 63. 4 50 420 5 0. 61 30. 5 t 179 59. 0 380 3 0. 60 42. 3 t 198 60. 4 480 3 0. 52 56. 3 2. 3 215 64. 6 420 3 0. 53 54. 0 1. 8 212 63. 0 350 5 0. 59 39. 2 t 181 57. 6

1 Normal pressure.

line insoluble material was remarkable, and a good pitch could not be obtained even if the reaction conditions for the third step were within the scope of this invention.

The yield of the pitch fractions by the process of this invention depends, as a matter of course, upon the properties of the raw materials and the treatment conditions, but it was generally in the range of 40-60% by weight based on the amount of the raw materials. The yield of pitch from the pitch fraction was usually in the range of 50-80% by weight of the pitch fractions.

A mixture of 100 parts of needle coke was prepared by coking the pitch fraction of Run No. 7 of the process of this invention and further heating it to 1300 C. 35 parts of coal pitch was extrusion-molded in an ordinary manner and then subjected to graphitization. The thermal expansion coefficient of the product was 1.6 l0- at 300-800 C. This value was similar to the thermal expansion coefficient of the articles prepared using an imported needle coke (1.6-2.0 l0- While this invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

What is claimed is:

1. A process of treating by-product oils obtained in the production of olefins which comprises treating the byproduct oils having boiling points of higher than 150 C. at temperatures of 400-600 C., for 10-1200 seconds tgider pressures of -200 kg./cm. separating said treated by-product oils into thermally stabilized oil fractions and residue fractions, and treating said residue fractions at temperatures of 300-480 C., for 1-10 hours under pressures of from normal pressure to 50 kg./cm. to provide pitch fractions.

2. The process of treating by-product oils as claimed in claim 1 wherein said by-product oil is obtained by thermally cracking a light petroleum fraction at 700- 950 C.

3. The process of treating by-product oils as claimed in claim 1 wherein said by-product oils are enriched in aromatics and contain more than 80% of fractions having a 'boiling point higher than 200 C.

4. The process of treating by-product oils as claimed in claim 1 wherein said first treating is at 440-580 C. for -500 seconds at SO -150 kg./Cm.

5. The process of treating by-product oils as claimed in claim 1 wherein the first treating reduces unsaturated bonds and decomposes long alkyl side chains in the byproduct oil, and the second treating dealkylates alkyl side chains which remain in the residue fraction and causes a polycyclic aromatization by polycondensation, whereby the pitch fractions having an aromatic structure are obtained.

6. The process of treating by-product oils as claimed in claim 1 further comprising removing light fractions having a boiling point lower than 400 C. to obtain a pitch.

7. The process of treating by-product oils as claimed in claim 1 wherein the thermally stabilized oil fractions are mainly composed of naphthalene and methyl naphthalene and the pitch fractions are mainly composed of polycyclic aromatics.

8. The process of treating by-product oils as claimed in claim 7 wherein the thermally stabilized oil fractions have a boiling point of 70350 C., a specific gravity of 0.9-1 and a refractive index lower than 1.68.

9. The process of treating by-product oils as claimed in claim 8 wherein from 30-50% by weight of the byproduct oil is yielded as the thermally stabilized oil fractions, which oil fractions comprise 40-90% by weight naphthalene and methyl naphthalene.

10. The process of treating byproduct oils as claimed in claim 7 wherein the pitch fractions yield is 40-60% by weight of the by-product oils, the pitch fraction comprising 5080% by weight pitch.

References Cited UNITED STATES PATENTS 2,752,290 6/ 1956 Beattie 208--131 2,944,958 7 1960 Goldthwait et a1 20876 3,537,976 11/ 1970 Alexander et al 208-76 3,617,477 11/1971 Gomi 208-40 3,617,515 11/1971 Bloomer 208-13 1 FOREIGN PATENTS 2,019,492 10/ 1970 Germany 2084 DELBERT E. GANTZ, Primary Examiner V. OKEEFE, Assistant Examiner U.S. Cl. X.R. 

